Many of the helicopters being operated today embody a dual-engine powerplant system. A dual-engine powerplant system enhances the normal flight capabilities of a helicopter, thereby increasing the utility of the helicopter for revenue flight operations. In addition, a significant feature inherent in a dual-engine helicopter is the capability of the dual-engine powerplant system to provide sufficient power to facilitate continued flight operations in safety, particularly take offs and landings (take offs and landings being the most critical segments of the helicopter flight envelope), in the event of a one engine inoperative (OEI) condition, e.g., a single-engine failure.
Since the OEI condition is statistically a low-occurrence event, the engines of a helicopter dual-engine powerplant system are designed primarily for dual-engine flight operations. That is, each engine is designed to specific power limits or ratings for dual-engine flight operations, e.g., a startup power rating, a take off power rating, a maximum continuous power rating (maximum power settings at which the engines may be continuously operated during dual-engine flight operations without incurring damage), a normal cruise power rating (power settings slightly lower than maximum continuous power rating that are typically established to comply with the engine maker's warranties), a 10-second transient power rating, and a 20-second transient power rating. During dual-engine flight operations, therefore, the helicopter is operated in such a manner that the design power ratings of the engines are not exceeded. In the sophisticated helicopters of today, the operation of the powerplant system is primarily controlled by a computer system (discussed in further detail hereinbelow), and such an engine computer control system typically includes protective logic routines (in the form of hardware, firmware, software, and/or combinations thereof) that automatically prevent the engine design power ratings from being exceeded during dual-engine flight operations.
A dual-engine helicopter that experiences an OEI condition, especially during a take off or landing, is subject to a potentially hazardous flight condition since the design power ratings of the single operative engine do not provide sufficient power for the safe operation of the helicopter under such a circumstance. Aviation regulatory authorities, therefore, have established general overdesign criteria for the powerplant system of a dual-engine helicopter to ensure that the helicopter can be safely operated utilizing a single operative engine during OEI flight operations. These criteria have resulted in the overdesign of the engines comprising the helicopter powerplant system so that a single operative engine is capable of providing a 30-second OEI power rating, a 2-minute OEI power rating, and a maximum continuous OEI power rating that ensure safe helicopter flight operations during OEI flight operations.
The overdesign of a dual-engine helicopter powerplant system to provide such OEI power ratings, however, is subject to antithetical considerations. On one hand, the greater the OEI power ratings overdesigned into the powerplant system, the larger the margin of safety with respect to helicopter flight operations during an OEI condition. Conversely, however, the greater the OEI power ratings overdesigned into the powerplant system, the larger are the costs, volume, and weight associated with the overdesigned powerplant system, particularly in light of the fact that the OEI power ratings are not utilized during dual-engine flight operations and the fact that an OEI condition is a low probability event.
Pragmatically, therefore, a helicopter dual-engine powerplant system is overdesign optimized to provide a margin of safety during helicopter OEI flight operations while concomitantly minimizing the costs, volume, and weight associated with the overdesigned dual-engine powerplant system. One consequence of this pragmatic design approach is that for a helicopter subjected to OEI flight operations, there is a statistically-significant probability, especially during utilization of the 30-second OEI power rating, that the single operative engine of the dual-engine powerplant system will be subjected to some degree of damage. Accordingly, for a helicopter subjected to OEI flight operations, there is a requirement that the dual-engine powerplant system be subjected to apposite maintenance procedures (at a minimum, inspection and maintenance; at a maximum, removal and replacement) prior to resuming dual-engine flight operations. While the pragmatic design approach described hereinabove is a logical solution to a complex situation, this approach is problematical when one considers helicopter pilot training requirements.
The objective of initial pilot certification and pilot refresher training is to ensure that pilots achieve and maintain a high degree of proficiency in all aspects of helicopter flight operations, including emergency procedures such as OEI flight operations. Such proficiency is typically achieved by repetitive training that is conducted under actual flight conditions, e.g., actual flight envelopes, actual gross weights (based upon pressure altitude and ambient temperature), actual power settings, actual instrument displays. An examination of the foregoing disclosure, however, should make it apparent that training in OEI flight operations under actual OEI flight conditions, particularly with respect to OEI flight operations utilizing the 30-second power rating, is not a realistic approach due to the possibility of sustaining some degree of engine damage during actual OEI flight operations. Therefore, approaches other than flight operations under actual OEI flight conditions have been developed to provide pilots with the required OEI flight training.
One approach to conducting OEI flight procedures training is to throttle one engine to an idle condition (to simulate an OEI condition) and conduct OEI flight procedures training utilizing the reduced power output of a "single operative engine". Typically, the reduced power output of the single operative engine is limited to a single power rating (as opposed to 30-second, 2-minute, and maximum continuous OEI power ratings available during actual OEI flight operations). The parametric indicators for the relevant engine operating factors provide display indications that are indicative of the actual reduced power outputs of the single operative engine, e.g., the power output prescribed by the single power rating.
Another approach involved conducting OEI flight procedures training utilizing both engines operating at an intermediate power output rating. In this approach, each engine is operated at a reduced power rating so that both engines in combination provide a power output at the intermediate power output rating that is equivalent to the power output provided by a single operative engine operating under the 30-second OEI power ratings. The parametric indicators of the relevant engine operating parameters provide display indications that are indicative of the actual reduced power outputs being provided by each engine.
Both of the foregoing exemplary approaches are deficient in one or more aspects. Each approach provides a single power output during OEI flight procedures training in contrast to the three power output levels provided by the helicopter powerplant system during actual OEI flight operations, e.g., the 30-second, 2-minute, and maximum continuous OEI power ratings. In addition, and perhaps more importantly from a training perspective, the status indicators for the relevant engine operating parameters provide display indications are limited to the prescribed power outputs of the approach, i.e., the displays indications are not totally consistent with the display indications that are relevant to actual OEI flight operations. In addition, there is no indication that conventional approaches to OEI flight procedures training are based upon correlated "training gross weights" for OEI flight procedures training to provide dual-engine helicopter handling characteristics that simulate the handling characteristics of a dual-engine helicopter subject to OEI flight operations while operating at an "allowable gross weight".
A need exists to provide a system and method for conducting OEI flight procedures training in a dual-engine helicopter that provides a high degree of realism, yet ensures a high degree of safety. Such a system and method should have a capability of providing a spectrum of reduced power outputs for OEI flight procedures training that realistically simulate the 30-second, 2-minute, and maximum continuous OEI power ratings that govern actual OEI flight operations. Furthermore, such a system and method should have the capability to provide display indications for selected engine operating parameters during OEI flight procedures training that correspond to the actual display indications perceived during OEI flight operations under actual 30-second, 2-minute, and maximum continuous OEI power ratings, even though the dual-engine helicopter is conducting OEI flight procedures training under reduced power outputs. In addition, the system and method should provide a mechanism for selecting "training gross weights" for OEI flight procedures training that are correlated with "allowable gross weights" so that the handling characteristics of a dual-engine helicopter subject to OEI flight procedures provides a high degree of realism to the handling characteristics of a dual-engine helicopter, which is operating at such allowable gross weights, that is subjected to OEI flight operations.